Rome, April 20 - Upper and Lower House lawmakers and representatives of Italy's regions on Saturday started voting in the sixth presidential ballot, in which President Giorgio Napolitano is expected to be re-elected. Napolitano agreed to stand for re-election after the five previous ballots failed to elect a successor to the 87-year-old because of rifts within the centre-left Democratic Party (PD), the biggest group in parliament. The PD, ex-premier Silvio Berlusconi's People of Freedom (PdL) party, the regionalist Northern League and outgoing Premier Mario Monte's Civic Choice party are all backing Napolitano for a second term. A simple majority of over half of the 1007 electors is needed. The anti-establishment 5-Star Movement, the third-biggest group in parliament, is set to keep voting for its candidate, Constitutional lawyer and former Communist party MP Stefano Rodota'. Rodota' also has the support of the left-wing SEL, which was allied with the PD in February's inconclusive general election.